The present invention relates to fluid directional control valves and particularly to such valves of the solenoid-operated type.
Solenoid-operated fluid directional control valves have application in a wide variety of hydraulically-operated apparatus. Typically, such valves are employed to control the flow of a supply of non-compressible fluid to and from the hydraulic cylinder of a hydraulic ram and provide for such purpose a fluid inlet port adapted to receive fluid under pressure from an arrangement of a pump and a fluid reservoir, a fluid outlet port adapted to direct the pressurized fluid to the hydraulic ram, and a fluid return port adapted to return the fluid from the ram to the inlet side of the pump. A spring-biased check valve provides fluid communication from the inlet to the outlet port while preventing flow in the reverse direction and a solenoid-operated check valve is arranged between the outlet and the return port to be normally closed by deenergization during operation of the hydraulic ram to prevent fluid flow into the return port and to be opened upon energization against the prevailing fluid pressure on the pump side of the solenoid valve to permit return flow of the fluid in the ram to the return port.
In many control valves of the above-described type, it is an important engineering consideration to maximize its return flow capacity through the solenoid-operated check valve thereof at low pressure drops while minimizing the force required of the solenoid to unseat the check valve against the fluid pressure operating oppositely against the check valve to permit the use of the smallest, least costly conventional solenoid possible for any given valve construction. While ball type check valves are ordinarily considered to provide superior sealing, longer life and fewer repair problems as compared to other conventional types of valves, conventional ball check valves characteristically require a greater unseating force for any given size seat than do other conventional check valve types under corresponding conditions of fluid pressure because of the spherical shape of the ball element whereby the ordinary ball retaining member used in such valves opposite the ball from the valve seat makes only limited, nonsealing contact with the ball whereby substantially the full surface area of the ball not extending into the valve seat is exposed to the fluid pressure against which any opening force must act. As a result, conical poppets have traditionally been used in check valves of the present type to reduce the unseating force required.
Accordingly, it is an object of the present invention to provide an improved ball-type check valve for a hydraulic fluid directional control valve adapted for solenoid operation which requires a substantially smaller unseating force than correspondingly sized conventional ball check valves and are comparable if not superior in such characteristic to conventional conical poppet check valves.